1. Field of the Invention
The invention relates to packet data transmissions between mobile and base radio stations, and more specifically to a method and system for calling mobile stations in a mobile radio network.
2. Description of the Prior Art
Connection-oriented concepts and concepts based on logic links may be used for transmitting data between two communications terminals. In the case of connection-oriented data transmissions, physical resources must be provided between the two communications terminals throughout the entire time of data transmission.
When transmitting data via logic links, there is no need for any permanent provision of physical resources. One example of such a data transmission is packet data transmission. In this case, there is a logic link between the two communications terminals throughout the duration of the overall data transmission, but physical resources are provided only during the times when data packets are actually being transmitted. This method is based on the data being transmitted in short data packets, between which relatively long pauses may occur. The physical resources are available for other logic links in the pauses between the data packets. The use of a logic link saves physical resources.
The packet data transmission method which is known from German Patent DE 44 02 930 may be used in particular for communications systems with limited physical resources. For example, in mobile radio systems such as the GSM mobile radio system (Global System for Mobile Communications), the physical resources in the frequency domainxe2x80x94the number of frequency channels and time slotsxe2x80x94are limited and must be used economically.
The GSM mobile radio system is one example of a time-division multiplex mobile radio system, in which time slots within a frequency channel may be split between different communications terminals. The radio station at the network end of a mobile radio network is a base station, which communicates with mobile stations via a radio interface. Transmission from a mobile station to the base station is called the uplink direction, and transmission from the base station to a mobile station is called the downlink direction. A channel, which is reserved for packet,data transmission, is formed by at least one time slot per time-division multiplex frame. A plurality of time-division multiplex frames in this case form a macroframe. Furthermore, the channel is governed by the carrier frequency and, possibly, by a frequency jump sequence.
The GSM mobile radio system was originally designed for voice transmission, although one channel was reserved for continuous information transmission between the mobile station and base station. However, for packet data transmission, a common packet data channel is used for packet data transmission for a plurality of mobile stations.
If one wants to transmit data from the network to the mobile station, that is to say, in the downlink direction, this mobile station is called by the network via the base station system (paging). To do this, time slots for calling are provided within the packet data channel, time slots for signalling messages, are required to set up a call, but no useful data are transmitted.
In this scheme the time interval between two successive call possibilities is the same for all mobile stations. But the waiting time between two successive call possibilities is too long for applications which require immediate data transmission.
In consequence, the invention is based on the object of specifying an improved method and an improved base station system for calling mobile stations in a mobile radio network. This object is achieved by the method having the features of forming a packet data channel by at least one time slot per time-division multiplex frame; forming a macroframe from a plurality of time-division multiplex frames; carrying out said packet data transmission from a plurality of said mobile stations via a common said packet data channel; providing at least one time slot for calling said mobile stations at cyclical intervals in said packet data channel; and setting a number of said time slots allocated within said macroframe for said mobile stations individually, where said.mobile stations are allocated to time slots for calling on the basis of subscriber-specific profiles and by the base station system having the features of a packet data channel that is formed by at least one time slot per time division multiplex frame; a macroframe that is formed by a plurality of time-division multiplex frames; a packet data transmission from a plurality of said mobile stations that are carried out via a common said packet data channel; at least one time slot for calling said mobile stations that is provided at cyclic intervals in said packet data channel; a control device for calling said mobile stations, said control device allocating said mobile stations to time slots for calling on the basis of subscriber-specific profiles, wherein a number of said time slots allocated within said macroframe for said mobile stations is set individually.
According to the invention, in the case of the method for calling mobile stations, mobile stations are allocated to time slots for calling on the basis of subscriber-specific profiles. The number of time slots allocated for calling within a macroframe can be set individually for the mobile stations.
This allows the requirement for time slots allocated for calling to be covered individually for each mobile station. For time-critical applications, shorter delay times can be achieved using the method according to the present invention. The number of time slots allocated for calling is governed on the basis of subscriber-specific profiles which are stored at the network end and/or at the mobile station end, and are signalled when required between the mobile station and the base station system.
According to an advantageous refinement of the invention, a plurality of groups are formed for calling mobile stations. A mobile station is allocated to one of these groups, and the groups can be allocated different numbers of time slots for calling within one cycle. The signalling complexity to form such groups is low, and group formation therefore allows the individual requirements of the mobile stations to be met quickly. Furthermore, it is advantageous if a mobile station is allocated to a plurality of groups at the same time. This allows a reduced delay time when calling to be achieved very easily for this mobile station.
According to an advantageous development of the invention, the association with the groups is signalled to the mobile stations by the base station. In this way, a changed requirement from the mobile station is satisfied quickly, flexibly and with only a small amount of signalling complexity.
The changed requirement is advantageously signalled by the mobile station to the base station system by changing its subscriber-specific profile, and the base station system then changes the mobile station""s allocation of time slots for calling. Subscriber-specific profiles, which may also be used for other resource allocations in a subsequent useful channel allocation, are particularly suitable as a criterion for the requirement for time slots for calling. Each mobile station may be allocated a specific profile independently of other mobile stations, and, in the process, the resource allocation by the base station system can be optimized, taking into account all of the mobile stations to be supplied.
In order to reduce the delay times for the mobile stations further, time slots for useful data transmission are also used as time slots for calling. One or more mobile stations may additionally be called via these time slots. The interval between two time slots for calling is thus shortened. Abbreviated identifiers which are transmitted in the time slots for useful data transmission expediently indicate the presence of calls for the mobile stations.
For mobile stations in which the time delays for a call are not critical, a long interval (possibly a number of seconds) may be set by a suitable allocation of time slots for calling. A mobile station can thus be switched between the time slots allocated to it for calling, in an energy-saving mode, reducing energy consumption of this mobile station and allowing relatively long operating times before the battery needs to be recharged. However, the application of the method according to the invention is not just limited to mobile called radio stations. The called mobile station may also be stationary.
According to advantageous further developments of the invention, the subscriber-specific profiles are designated by different qualities of service. These qualities of service are, for example, for the GSM mobile radio network, standardized identifiers of a packet data transmission which can also easily be used for the method according to the invention. As an alternative to this, the subscriber-specific profiles are designated by different services used by the mobile station. The delay which is still acceptable or even desirable can easily be determined as well on the basis of the service to be used, for example E-mail (relatively long delay) or electronic train control (short delay). In addition, it is possible to base the allocation of time slots for calling on the number of mobile stations registered in the radio area of the base station system. This knowledge can be included in an improved allocation strategy.
Further advantageous refinements of the subscriber-specific profiles are designated by different priorities, by different permissible delay times or by different required data rates for packet data transmission. The permissible intervals between two time slots allocated to the respective mobile station for calling may be read directly from these values.